1. Field of the Invention
The present invention relates to an optical disk drive, and more particularly, to an optical disk drive including an optical pickup actuator employing a Lorenz force generated in a coil by electromagnetic induction.
2. Description of the Related Art
In general, an optical disk drive writes information by scanning light onto a disc that is a recording medium or reads information from the disc. The optical disk drive includes a spindle motor that rotates a disc and an optical pickup that records information on, or reproduces information from, a recording surface of the disc by emitting light onto the recording surface.
Typically, an optical pickup has an actuator for controlling the position of an objective lens in a focus and a tracking direction so that light is focused on a desired track formed onto a recording surface of the disc. The optical pickup actuator serves as a controller by constantly adjusting the distance between the objective lens and the recording surface so that the focus of a light spot is maintained and the light spot follows the desired track.
FIG. 1 is a perspective view of a conventional optical pickup actuator, and FIG. 2 is a top view of the optical pickup actuator of FIG. 1. Referring to FIG. 1, a blade 3 on which an objective lens 4 is mounted is positioned on a base 1 in such a way as to be elastically movable by wires 6. First coils 11a and 11b and second coils 12a and 12b are positioned on the blade 3. While the first coils 11a and 11b are wound in a vertical direction and positioned in a Y-direction symmetrically with respect to the objective lens 4, the second coils 12a and 12b are wound in a horizontal direction and positioned in an X-direction symmetrically with respect to the objective lens 4.
Magnets 21a, 21b, 22a, and 22b are also mounted on the base 1. While the magnets 21a and 21b are disposed opposite the first coils 11a and 11b, respectively, the magnets 22a and 22b are disposed opposite the second coils 12a and 12b, respectively.
In FIG. 1, X, Z, and T directions represent tracking, focusing, and tilt directions, respectively.
A description of an operation of actuating the blade 3 in a tracking direction X follows. As shown in FIG. 2, when current is supplied to the first coils 11a and 11b, an electromagnetic force Fx is induced in the first coils 11a and 11b by an interaction with the magnets 21a and 21b. If current is applied to the first coils 11a and 11b in an opposite direction to the direction marked in FIG. 2, then an electromagnetic force −Fx is induced in the first coils 11a and 11b. By controlling the direction that current is applied to the first coils 11a and 11b, the driving of blade 3 in a tracking direction X is controlled.
A description of the operation of actuating the blade 3 in a focusing direction Z follows. If current is supplied to the second coils 12a and 12b in the directions A1 and A3, respectively, an electromagnetic force Fz acting in upward +Z direction is induced in the second coils 12a and 12b by interaction with the magnets 22a and 22b. If current is applied to the second coils 12a and 12b in the directions A2 and A4, respectively, an electromagnetic force −Fz acting in downward −Z direction is induced in the second coils 12a and 12b. By supplying the current to the second coils 12a and 12b in directions A1-A3 or A2-A4, the blade 3 is driven in a focusing direction Z.
A precisely focused light spot is created only when light exiting through the objective lens 4 is incident perpendicularly to the recording surface on the disc. Otherwise, it is not possible to create a precise light spot on the disc, which may cause an error in recording data on, or reproducing data from, the disc.
Adjusting an incident angle of light so that the light is perpendicular to the recording surface of a disc is referred to as tilt or skew adjustment. Since an ability to dynamically adjust tilt is required for precise recording or reproduction, an optical pickup actuator also requires an ability to adjust in a tilt direction.
The operation of driving the blade 3 in a tilt direction T in the conventional optical pickup actuator of FIG. 1 is as follows. Actuation in the tilt direction T is performed by inducing electromagnetic forces in the second coils 12a and 12b in opposite directions. That is, if current is supplied to the second coils 12a and 12b in directions A1 and A4, respectively, then an electromagnetic force Fz acting upward is induced in the second coil 12a while an electromagnetic force −Fz acting downward is induced in the second coil 12b. Furthermore, where current is applied to the second coils 12a and 12b in directions A2 and A3, respectively, electromagnetic forces −Fz and Fz acting in upward and downward directions are induced in the second coils 12a and 12b, respectively. By supplying current to the second coils 12a and 12b in directions A1-A4 or A2-A3 in this manner, the blade 3 is driven in the tilt direction T.
The wires 6 not only elastically support the blade 3 on the base 1 but also serve as a path for supplying current to the first coils 11a and 11b and the second coils 12a and 12b. FIG. 1 shows four wires 6, and hinges 7, connecting with the wires 6, formed on the blade 3. The four wires 6, in two pairs, supply current to the first coils 11a and 11b and second coils 12a and 12b. This configuration is designed for actuation only in the focusing and tracking directions Z and X. To enable actuation in the tilt direction T, in addition to the above, current needs to be supplied separately to the second coils 12a and 12b in different directions. Thus, although not shown in the drawings, a further pair of wires are needed. Likewise, in a case where a third coil (not shown) is positioned on the blade 3 for actuation in the tilt direction T, an additional pair of wires are required.
Since the center of gravity of the blade 3 supported by the wires 6 needs to be considered, the placement of the hinge 7 is critical. As shown in FIG. 1, the four wires 6, sufficient only for actuation in focusing and tracking directions Z and X are coupled with two hinges that are formed on either an upper or a lower surface of the blade 3. However, if further actuation is required in the tilt direction T, two additional wires are needed. With the conventional optical pickup actuator of FIG. 1, coupling two additional hinges with the two wires is difficult since the first and second coils 11a, 11b, 12a, and 12b are positioned around the four sides of the blade 3.
In the conventional optical pickup actuator as described above, the magnets 21a, 21b, 22a, and 22b are positioned in four directions around the blade 3. In particular, the magnets 22a and 22b, for actuation in the focusing and tilt directions Z and T, are positioned in the tracking direction X, i.e., in a radial direction of the disc (not shown) in the optical disk drive having an optical pickup actuator. This poses a limitation in that the optical pickup actuator needs to be designed to avoid interference with a spindle motor (not shown) for rotating the disc. A recent increase in demand for super-slim disk drives requires further miniaturization and lightweight structure, i.e., by reducing the number of parts of an optical pickup actuator. Furthermore, an increase in the optical recording density requires improvement in sensitivity of actuation in tracking and tilt directions X and T.